1. Field of the Invention
The present invention relates to a direct memory access (DMA) channel control apparatus which can assign independent DMA transfer control lines in units of expansion slots while maintaining the compatibility of the expansion slots with the existing information processing apparatuses.
2. Description of the Related Art
In conventional information processing apparatuses and the like, an expansion card is used as one of expansion means for the expansion of the function or the like. An expansion card is inserted in an expansion slot serving as a connector in a conventional control apparatus. All the expansion slots are connected such that pins of the same numbers are connected in parallel to each other by various signal lines. The expansion slots are also connected in parallel with a direct memory access controller (DMAC). DMA transfer control lines are also connected between the expansion slots in parallel. A CPU sends status and address signals, respectively serving to generate timing and address signals, to a decoder. The decoder generates required signals, i.e., an I/O write command (IOWCO), an I/O read command (IORCO), and a chip select signal (CSO). Each command is supplied to the main body of the apparatus together with external data to be interpreted, thus executing a predetermined expanded function. In this conventional apparatus, the same result can be obtained whichever slot the expansion card is inserted into.
Conventionally, in order to maintain the compatibility with an expansion card used for the existing information processing apparatuses and the like, signal lines for the respective pins of the slots cannot be changed, and the number of signal lines is limited. Therefore, if the required number of expansion slots is large, the number of DMA transfer control lines is smaller than that of the expansion slots. Even in a case wherein the number of expansion slots is small, if the DMA transfer control lines in the main body of the apparatus are also used as the DMA transfer control lines of the expansion slots, the number of DMA transfer control lines which can be actually used for the expansion slots is reduced. For this reason, if independent DMA transfer control lines are to be assigned to the respective expansion cards, i.e., the respective expansion slots, a shortage of DMA transfer control lines occurs. In contrast to this, if DMA transfer control lines are independently connected in units of expansion slots, the compatibility of software for processing the contents of an expansion card in the existing apparatus is lost since the specifications of a DMA transfer control line for each expansion slot are different from those of a corresponding expansion slot of an existing apparatus.